1. Technical Field of the Invention
The present invention relates to a discharge lamp drive apparatus which drives discharge lamps used as a backlight for a liquid crystal, and a liquid crystal display apparatus.
2. Description of the Related Art
In recent years, with an increase in size of a screen of a liquid crystal panel, a circuit scheme which drives a plurality of discharge lamps for a backlight in parallel has been used in one liquid crystal panel. As means for driving the plurality of discharge lamps in parallel, there are a scheme which connects one end side of the plurality of discharge lamps with an inverter circuit and a transformer and connects the other end side of the same with a GND (which will be referred to as a normal drive scheme hereinafter) and a scheme which connects one end side of the plurality of discharge lamps with a first transformer and connects the other end side of the same with a second transformer so that both the transformers are driven in common by using one inverter circuit and the discharge lamps are driven from both sides (which will be referred to as a differential drive scheme hereinafter).
Of these two schemes, according to the differential drive scheme, since an output voltage of the inverter circuit can be reduced and a circuit component having a small withstand voltage can be used, thereby decreasing a cost.
Meanwhile, in a discharge lamp drive apparatus, there occurs a state in which a current does not flow between a transformer and discharge lamps (which will be referred to as an open state hereinafter) in some cases because of, e.g., a contact failure of a discharge lamp electrode with respect to a connector. In such an abnormal state, since a normal liquid crystal display operation cannot be obtained, this state must be detected. As such means, for example, Patent Reference 1 discloses a normal drive type discharge lamp drive apparatus which is provided with a light-off detection circuit which detects the open state.
The discharge lamp drive apparatus disclosed in Patent Reference 1 adopts the normal drive scheme, and the other end side of discharge lamps connected with the GND has a low voltage. Therefore, a resistance is provided between the other end side of the respective discharge lamps and the GND, and a current flowing through the resistance is detected, thereby detecting whether each discharge lamp is in the open state.
However, in case of a discharge lamp drive apparatus adopting the differential drive scheme, since transformers are connected with both ends of the discharge lamps and both the ends of the discharge lamps have a high voltage, it is impossible to take such a circuit configuration as disclosed in Patent Reference 1 in which the resistance is provided between the discharge lamps and the GND.
Further, since the discharge lamp drive apparatus of Patent Reference 1 has a configuration which detects whether each of the plurality of discharge lamps is in the open state, the number of components is increased, and hence a cost cannot be reduced.
Patent Reference 1: Japanese Patent Application Laid-open No. 267674-1994